A cross-layer scheduling scheme for SDMA systems with limited feedback

The cross-layer scheduling problem in multi-antenna broadcast channel with more singe-antenna receivers than transmit antennas and partial channel state information at the transmitter (CSIT) is investigated. A gradient-based scheduling framework is formulated. The proposed scheduling scheme can efficiently support the services with diverse quality of service (QoS) requirements. According to the channel state information (CSI) which is feedback from the mobile station and the queue state information (QSI) which is obtained from the upper layer, the proposed algorithm dynamically assigns the transmit mode (i.e., the number of the users to serve) to maximize the system throughput by fully exploiting the multiplexing gain and the multiuser diversity gain. The simulation results show that the proposed algorithm significantly improves the system performance in terms of the system throughput, packet dropping probability, and the ratio of unsatisfied minimum data rate of non-real-time services. The effect of the fairness factor is also evaluated by simulations.